[FEATURE]: Fall back to OSC 9 desktop notifications when OSC 99 is unsupported (Zed, Ghostty, etc.)

Summary

In terminals that support OSC 9 (or OSC 777) but not OSC 99, opencode never shows desktop notifications — only the attention sound plays.

Environment

• opencode v2.0.10
• Linux (KDE Plasma / Wayland)
• Terminal: Zed 1.20.2 integrated terminal
• Config: attention: { enabled: true, notifications: true, sound: true }

What happens

• The attention sound plays as expected.
• No desktop notification is ever shown.

Root cause (investigated)

Notification support is detected in OpenTUI's native layer, which probes for OSC 99 (\x1b]99;i=opentui-notifications:p=?;\x1b\\) and iTerm2 OSC 1337;Capabilities. renderer.triggerNotification returns false until notification capability is detected, and notifications are only ever emitted as OSC 99 — there is no OSC 9 / OSC 777 fallback.

Zed added OSC 9 desktop notification support in zed-industries/zed#58014 (merged 2026-06) but does not implement OSC 99 or iTerm2 OSC 1337. Therefore capabilities.notifications stays false, and packages/tui/src/attention.ts silently skips the notification path.

The same limitation applies to other OSC 9/777-only terminals: Ghostty, Warp, VS Code integrated terminal, WezTerm (OSC 777 only for notifications), etc.

Proposal

When OSC 99 capability is not detected, fall back to emitting OSC 9 (\x1b]9;<message>\x07). It is widely supported (kitty, Zed, Ghostty, WezTerm, foot, iTerm2, Warp) and harmless when ignored.

This could live either in packages/tui/src/attention.ts (when triggerNotification returns false) or in OpenTUI's native notification path, alongside the existing OSC 99 support.

Related

• #35055 — desktop notifications silently suppressed when terminal focus tracking is unavailable (related failure mode, closed not_planned)
• anomalyco/opentui#1067 — OSC 99 probes restricted to XT_VERSION-identified terminals
• anomalyco/opentui#1333 — focus reporting gated on a DECRQM answer

Start in packages/tui/src/attention.ts and trace the notification path when renderer.triggerNotification returns false; then inspect OpenTUI’s native notification path and its existing OSC 99 capability handling. Done means OSC 9 is emitted for terminals without detected OSC 99 support while existing OSC 99 behavior remains intact; verify the notification and sound behavior in the described terminal scenarios.